Diamond-like Nanocomposite Coatings Research Articles

Influence of structure and composition of diamond-like nanocomposite coatings on cell viability

This paper investigates the influence of the structure and properties of diamondlike nanocomposite (DLN or a-C:H:SiOx) coatings synthesized by plasma-assisted chemical vapor deposition on cell viability and coating biocompatibility. The structure and properties of the DLN coatings are changed by the negative pulse amplitude of the bipolar bias voltage of the substrate. The structure of the obtained DLN coatings is studied by Fourier-transform infrared spectroscopy and Raman spectroscopy. Atomic force microscopy provides angstrom-level surface-profiling information. The microhardness testing of the DLN coatings is performed on a nanohardness indenter of a three-sided Berkovich pyramid. It is shown that the higher roughness of the substrate surface, the growth in the crystalline graphite content in the coating, and Si—C bonds improve the DLN coating biocompatibility deposited at a −500 V bias voltage and the cell viability (>98% of HeLa cells), resulting in a lower cell death (1–2%). It is demonstrated that DLN coatings can be applied in biomedicine.

Tribological Performance of Diamond-like Nanocomposite Coatings: Influence of Environments and Laser Surface Texturing

Diamond-like nanocomposite (DLN) films (a-C:H:Si:O films) are characterized by their unique structure and remarkable tribological properties to be pronounced under various environmental and surface modification conditions. In this paper, we investigated the effects of environments (humid air, water and oil lubrication, elevated temperatures) and laser surface texturing on tribological performance of DLN coatings. Femtosecond laser (wavelength 515 nm) was used for surface texturing. Comparative tests of DLN films sliding against different counterbodies (steel, Si3N4) in humid air and water demonstrated the low-friction and low-wear performance under water, in the absence of chemical interaction of water with the counterbody surface. The wear rates of the film and Si3N4 ball in water, 7.5 × 10−9 and 2.6 × 10−9 mm3/(Nm), were found to be considerably lower than the corresponding values 6.8 × 10−7 and 3.8 × 10−8 mm3/(Nm) in humid air, in spite of higher friction in water-lubricated sliding. Laser surface texturing of DLN films was performed to fabricate microcrater arrays, followed by tribological testing under oil lubrication at different temperatures, from 23 to 100 °C. The lubricated friction performance of laser-textured films was improved at both the room temperature and elevated temperatures. The friction coefficient was reduced from 0.1 (original film) to 0.083 for laser-textured film at room temperature, and then to 0.068 at 100 °C. The nano-/microfriction behavior of laser-structured surface characterized by lower friction forces than the original surface was demonstrated using friction force microscopy in ambient air. The obtained results demonstrate excellent tribological properties of DLN coatings in various environments, which can be further improved by femtosecond-laser-surface texturing.

Femtosecond-laser-ablation induced transformations in the structure and surface properties of diamond-like nanocomposite films

Femtosecond laser ablation processing is applied for surface modification and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films). Using a visible femtosecond laser (wavelength 515 nm, pulse duration 320 fs), microgroove patterns have been fabricated on the DLN films, aimed at further studies of their properties. The studies were focused on (i) structural transformations in the surface layers using Raman spectroscopy and transmission electron microscopy (TEM), (ii) wettability of laser-patterned films, and (iii) nano/microscale friction properties of laser-patterned DLN films using lateral force microscopy. Raman spectroscopy and TEM data showed characteristic features of the surface graphitization during ultrashort-pulse ablation. High resolution TEM study of the microgrooves revealed the formation of cubic SiC nanocrystals (4–8 nm size) on the laser-ablated surface. The water contact angle measurements showed anisotropic wetting behavior of the grooved surfaces (the contact angle was different in the directions parallel and perpendicular to microgrooves), depending on the groove depth (aspect ratio). Lateral force microscopy examination (with micro-sized Si tips) showed that the laser-patterned regions exhibited low friction properties compared to the original surface. The obtained results demonstrate that femtosecond laser processing is an effective technique to generate new properties of hard DLN coatings at the micro and macroscale.

Femtosecond laser surface texturing of diamond-like nanocomposite films to improve tribological properties in lubricated sliding

We report on femtosecond laser ablation and surface micropatterning (texturing) of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films), aimed to improve tribological properties of laser-patterned films under lubricated sliding conditions. Femtosecond laser system generating pulses of 320-fs duration at the wavelength 515 nm is applied. Femtosecond laser ablation of 2.7-μm-thick DLN films is studied to determine optimum irradiation parameters for laser surface texturing with the requirements of the minimal spot size, high ablation rate, surface quality and pattern depth less than the film thickness. Periodic microcrater patterns (with 10 μm diameter, 2.2 μm depth, and different area density of microcraters) have been fabricated on the DLN films over the areas of 6 mm × 10 mm size. Tribological tests of the original and laser-patterned DLN films are performed using a ball-on-flat tribometer under linear reciprocating sliding against 100Cr6 steel balls in the presence of oil lubrication (engine oils of low and high viscosity). The ball-on-flat investigations have demonstrated the reduced friction and wear properties of the laser-textured DLN films, depending on the area density of microcraters and lubrication conditions. The obtained results evidence that femtosecond laser surface texturing is an effective technique to improve lubricated sliding performance of the DLN coatings.

Deposition and characterization of diamond-like nanocomposite coatings grown by plasma enhanced chemical vapour deposition over different substrate materials

Diamond-like nanocomposite (DLN) coatings have been deposited over different substrates used for biomedical applications by plasma-enhanced chemical vapour deposition (PECVD). DLN has an interconnecting network of amorphous hydrogenated carbon and quartz-like oxygenated silicon. Raman spectroscopy, Fourier transform–infra red (FT–IR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) have been used for structural characterization. Typical DLN growth rate is about 1 \({\upmu} \)m/h, measured by stylus profilometer. Due to the presence of quartz-like Si:O in the structure, it is found to have very good adhesive property with all the substrates. The adhesion strength found to be as high as 0·6 N on SS 316 L steel substrates by scratch testing method. The Young’s modulus and hardness have found to be 132 GPa and 14· 4 GPa, respectively. DLN coatings have wear factor in the order of 1 × 10 − 7 mm3/N-m. This coating has found to be compatible with all important biomedical substrate materials and has successfully been deposited over Co–Cr alloy based knee implant of complex shape.

The role of substrate plasticity on the tribological behavior of diamond-like nanocomposite coatings

Finite-element modeling (FEM) was used to predict the contact stress at which the transition from elastic to plastic deformation occurs in a metallic substrate underneath a hard tribological coating. Using model systems of diamond-like nanocomposite (DLN) coatings on electroformed Ni, NiMn alloy and Inconel 718, friction measurements were made at contact stresses ranging from 540 to 1720MPa. Cross-sections of wear scars suitable for visualization of friction-induced plastic deformation in the substrate were prepared by focused ion beam microscopy and analyzed by electron backscatter diffraction. At contact stresses below the FEM-predicted elastic–plastic limit, the coefficient of friction decreased linearly with increase in contact stress, suggesting that interfacial shear is the major mechanism of friction in DLN. Contact stresses above the FEM-predicted elastic–plastic limit resulted in plastic deformation of the metallic substrate, and in extreme cases fracture and removal of the coating resulting in a sudden increase in friction.

Mechanisms of friction in diamondlike nanocomposite coatings

Diamondlike nanocomposite (DLN) coatings (C:H:Si:O) processed from siloxane precursors by plasma enhanced chemical vapor deposition are well known for their low friction and wear behaviors. In the current study, we have investigated the fundamental mechanisms of friction and interfacial shear strength in DLN coatings and the roles of contact stress and environment on their tribological behavior. Friction and wear measurements were performed from 0.25to0.6GPa contact pressures in three environments: dry (<1% RH) nitrogen, dry (<1% RH) air, and humid (50% RH) air, with precise control of dew point and oxygen content. At 0.3GPa contact stress, the coefficient of friction (COF) in dry nitrogen was extremely low, ∼0.02, whereas in humid air it increased to ∼0.2, with minimal amount of wear in both environments. The coatings also exhibited non-Amontonian friction behavior, with COF decreasing with an increase in Hertzian contact stress. The main mechanism responsible for low friction and wear under varying contact stresses and environments is governed by the interfacial sliding between the DLN coating and the friction-induced transfer film adhered to the ball counterface. This interfacial shear strength, computed from COF-inverse Hertzian contact stress plots, was found to be 9MPa in dry nitrogen and 78MPa in humid air. Time-of-flight secondary ion mass spectroscopy analysis of the interfaces (wear tracks and transfer films) was used to explain the tribochemical effects in both environments. The transfer films generated in humid air were found to be enriched with SiO2 containing fragments, whereas those formed in dry nitrogen had hydrogenated and long range ordered carbons with practically no SiO2 fragments, ultimately resulting in much lower interfacial shear strength and COF.

Thermal stability evaluation of diamond-like nanocomposite coatings

Diamond-like nanocomposite (DLN) is a class of modified diamond-like carbon (DLC) coatings. The DLN films consist of amorphous networks of carbon and silicon, which are made by incorporating the Si–O structures into the DLC films. The thermal stability of DLN films was investigated by annealing the films deposited on Si (1 0 0) substrates by plasma enhanced chemical vapor deposition. The films were heated in ambient air for 1 h at the annealing temperatures ranging from 200 to 600 °C. The mechanical properties as well as structural modification of the annealed films were investigated as a function of annealing temperature. The chemical structure, composition, thickness and hardness values of the annealed films were measured by Raman spectrometer, electron probe micro analyzer, scanning electron microscope and ultra micro-indentation system, respectively. The comparison between DLN and DLC films on their thermal stability was made in order to understand the characteristics of DLN films. It is assumed that the DLN films show a good thermal stability for the protective coating applications at high temperature environment in air atmosphere in comparison with DLC films.

Role of Third Bodies in Friction Behavior of Diamond-like Nanocomposite Coatings Studied by In Situ Tribometry

The friction and wear behavior of amorphous diamond-like nanocomposite (DLN) coatings (C:H:Si:0) in low speed, dry sliding contact has been investigated using a home-built in situ tribometer. Tests were performed under reciprocating sliding against sapphire and steel hemispheres in dry (∼4% RH) and moist (35 to 52% RH) air at contact stresses of 0.7 and 1.1 GPa. In situ visual observations identified how third body processes affected the friction behavior of DLN coatings. For all test conditions, a transfer film began to form on the sapphire hemisphere during the first cycle, and the coefficient of friction dropped during further buildup of the transfer film. Video analysis showed most of the sliding motion took place between the transfer film on the hemisphere and the DLN coating. This velocity accommodation mode, interfacial sliding, was responsible for steady-state friction coefficients between 0.03 and 0.05 with lower values obtained at high stress and low RH. When the transfer film broke up the friction began to spike (0.1 ≤ μ ≤ 0.5); during the spikes, shearing of third bodies also contributed to velocity accommodation, as debris attached, detached and recirculated between the hemisphere and the track. Subsequently, the friction coefficient fluctuated between low and high values due to reformation and breakup of the transfer film, respectively.

Tribological properties of diamond-like nanocomposite coatings at high temperatures

Abstract Diamond-like nanocomposites (DLN) films are amorphous and consist of C, H, Si, and O. In addition, metal atoms can be incorporated into the coatings. The DLN coatings exhibit a low coefficient of friction, low wear rate, low stress, high hardness and good adhesion on a variety of substrates. The thermal stability of DLN films deposited on silicon substrates was investigated after the samples had been thermally annealed in air and argon atmospheres. The sample analysis by micro-Raman spectroscopy, nano-indentation and ball-on-disk tribometry are reported here. The investigation revealed that the performance of DLN films from a tribological perspective is very good up to 400°C in air. The hardness of the DLN films showed a decrease of less than 15% up to 400°C in air. The wear rate of the DLN films was at or below 10 −7 mm 3 /Nm up to 400°C in air.

Sliding wear behavior of diamond-like nanocomposite coatings

Abstract Diamond-like nanocomposites (DLN) are a class of amorphous thin film material consisting of a diamond-like carbon (a-C:H) network and a glass-like a-Si:O network. The sliding wear behavior of 1–2-μm-thick DLN coatings on Si was studied using WC and steel balls in ambient air (RH=30–50%) at initially high contact stresses (0.8 GPa). The hardness of the DLN coatings, 9–17 GPa, was greater than that of steel (8 GPa) but less than that of WC (16 GPa). The friction coefficients for both couples were between 0.04 and 0.06, and the endurances were from 30 000 to 200 000 cycles. Despite the similarities, the wear behavior of the steel/DLN and WC/DLN couples differed: in the former, the steel balls wore, producing lower stresses but wider and deeper wear tracks; in the latter, the WC ball did not wear, and the wear tracks were narrower and wore uniformly. The latter wear behavior allowed wear rates for DLN to be determined. The wear of the DLN was measured at regular intervals during extended ball-on-disk testing. DLN was shown to wear at a constant rate, i.e. linearly with number of cycles, and to have wear factors in the range of 2×10−8–1.1×10−6 mm3 N−1 m−1.

Diamond-like nanocomposite coatings for low-wear and low-friction applications in humid environments

Diamond-Like Nanocomposite (DLN, Dylyn®) coatings are amorphous, hard and wear resistant coatings, deposited using a plasma-assisted CVD process. These coatings consist of two interpenetrating networks, one being a diamond-like carbon (a-C:H) network and the other a glass-like a-Si:O network. This specific structure leads to lower internal stress, better adhesion and higher temperature stability as compared to diamond-like carbon. The structure and bonding type were investigated using grazing-incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS), respectively. The coefficient of friction of Diamond-Like Nanocomposites, as measured in a standard ball-on-disk tribometer using a steel counterbody, is typically 0.04 to 0.08 in air of 50% relative humidity (RH). Even in humid air of 90% RH and under water, the coefficient of friction stays below 0.1. The wear factor of Diamond-Like Nanocomposite coatings was determined using profilometric measurements of the wear track after a ball-on-disk test and is typically 2×10 −7 mm 3/N m. Under water, an extremely low wear factor, below 5×10 −8 mm 3/N m, was measured. This low-friction and low-wear behaviour of Diamond-Like Nanocomposite coatings, also in humid environments, enables industrial applications of these coatings as hard, self-lubricating coatings on sliding parts in the automotive, chemical, pharmaceutical or biomedical industry.

Diamond-like nanocomposite coatings (a-C:H/a-Si:O) for tribological applications

Abstract Diamond-like nanocomposite (DLN) coatings (a-C:H/a-Si:O) are a particular class of modified diamond-like carbon coatings, which can be predominantly described as two interpenetrating amorphous networks, one network being a diamond-like a-C:H network and the other a glass-like a-Si:O network. Structural studies have been performed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The two-network description of the atomic bonding state is investigated by analysing the CC, CSi and SiO contributions to the C 1s and Si 2p XPS photolines. Tribological properties have been measured using standard ball-on-disk tests against a steel counterbody at 10 N load, yielding a typical wear factor between 0.5 and 4 × 10−7 mm3 Nm−1. The coefficient of friction against steel is typically between 0.05 and 0.15, even in humid air and under water. The low-friction and low-wear DLN coatings, combined with low internal stress and good adhesion, make this type of coatings an excellent candidate for many tribological applications in the automotive, textile, chemical or biomedical industry.

Metal Doping Tailors the Electrical, Mechanical, and Optical Properties ofDiamondlike Nanocomposite Coatings for Many Applications

(1998). Metal Doping Tailors the Electrical, Mechanical, and Optical Properties of Diamondlike Nanocomposite Coatings for Many Applications. Materials Technology: Vol. 13, No. 3, pp. 93-96.

Porosity Evolution in Electrosurgical Blade Coatings

AbstractDuring Electrosurgery, Radio Frequency (RF) electrical power is applied to a cutting surface which cauterizes the incision. The desiccation of surrounding tissue results in hemostasis and surgery without bleeding. In the case of localized heavy bleeding, a coagulation process is employed using modulated RF power. However, substantial amounts of desiccated tissue may stick to the blade, undoing the achieved hemostasis, and possibly worsening the situation. To prevent this, various electrosurgical blade coatings have been developed to both permit the flow of RF power through the coating, and prevent desiccated tissue from sticking to it.PolyTetraFluoroEthylene (PTFE) is a commonly used electro- surgical blade coating that undergoes substantial surface morphology changes during use, eventually leading to failure. Highly conductive Diamond-Like Nanocomposite (DLN) electrosurgical coatings have been developed with the requisite non-stick characteristics and enhanced durability.After a brief review of electrosurgical fundamentals, the underlying mechanisms of operation of these two coating materials are compared. In the case of PTFE, establishment and evolution of porosity in the coating is essential to the flow of RF power, yet ultimately leads to long term degradation. Alternate conduction mechanisms for DLN coatings are considered.

Electrical properties of diamond-like nanocomposite coatings

Diamond-like nanocomposite (DLN) films comprising of C, H, Si, O and metal atoms were deposited on metallized silicon substrates via an accelerated plasma approach. The films were investigated by Raman spectroscopy, Fourier transform infrared spectroscopy and Rutherford backscattering. The film resistivity, dielectric constant, electrical breakdown and current-voltage hysteresis characteristics were measured using metal-insulator-metal heterostructures. Results indicate that DLN film resistivities can be tailored over 16 orders of magnitude (10 14–10 −2 Ω-cm). Current-voltage measurements yielded breakdown strengths larger than 10 6 V/cm. The dielectric constant of the films investigated ranges from 3 to 8. Capacitance-voltage characteristics and the effect of temperature cycling was also studied. The properties of electrical tailorability and diamond-like properties make DLN a suitable candidate for applications requiring both wear resistance and electrical tailorability.